1. Introduction
This invention relates generally to apparatus for maintaining and growing biological cells ex vivo and, more particularly, to apparatus of this kind that maintains and grows the cells in a portable cassette while maintaining a sterile system that is closed to the external environment.
Many medical disorders can now be resolved by using transplanted cells, tissues, or organs. Transplantation has evolved from the surgical transfer of tissue from the one part of a patient's body to another, to the surgical transfer of organs and tissues between individuals, to the transplantation of blood and immune systems between individuals. With increased demonstration of the medical benefit of tissue transplantation, the demand for organs and tissues suitable for these procedures has far exceeded the availability. Furthermore, in those cases where availability is less an issue, e.g., bone marrow, the procedure is cost prohibitive and can be invasive for the donor or the patient.
As an evolution of the clinical need, two related fields have evolved, which have been termed "cell therapy" and "tissue engineering." Cell therapy generally refers to the use of living cells, rather than drugs, to treat a clinical disorder or disease. Perhaps the most widely practiced form of cell therapy today is with bone marrow or hematopoietic stem cell transplantation in patients who have received hematopoietic toxic chemotherapy or radiation. This procedure involves the reinfusion of early stage cells that originate in the bone marrow, so that these cells can reestablish a patient's blood and immune system, and often the bone marrow tissue as well. Through this cell therapy process, the hematopoietic toxicity from cancer treatment is remedied.
Tissue engineering generally refers to the utilization of different disciplines between engineering, physiology, and cell biology, to develop at least a partially living tissue that is capable of normal tissue function. Once produced, this tissue may be transplanted into humans to restore or improve normal tissue or organ function. Numerous biotechnology companies are engaged in projects to engineer human tissues for transplantation.
For both cell therapy and tissue engineering procedures, there is a critical need to be able to process and/or produce ex vivo the cells that will be used for the therapeutic transplant. Biological science has now progressed such that, for many of the human tissues, methodology has been developed so that the key cells of that tissue can be grown outside the body. As a result, a clinically useful amount of tissue can be generated from a small amount of starting material, which is obtained with a minimally invasive technique. With this achievement, the opportunity for increasing and more diverse use of tissue transplantation is offered.
In parallel with this advancement, and largely dependent upon its success, are the numerous gene therapy approaches being advanced to initial clinical trials that involve the ex vivo genetic manipulation of cells and tissue. Gene therapy involves transduction of the genome of the cell to achieve correction of a defective gene, regulation of a disease condition, or production of a beneficial molecule. Those gene therapy procedures that will benefit from ex vivo administration of a gene vector to an expanded or donor tissue in order to enhance the targeting of the gene and avoid this systemic administration (likely to include most conceivable gene therapies for the next decade or longer) will be well served by the above advancements in tissue genesis and production.
The particular physical and biological requirements for the production of cells and tissues of blood, skin, cartilage, bone, pancreas, the nervous system, and various other endothelial and mesenchymal tissues of interest to cell and genetic therapists, will vary. However, two key components are necessary in order to grow cells and tissues ex vivo: 1) cells of self or donor origin that are capable of replicating and differentiating, as needed, for the formation of functioning tissue; and 2) an ex vivo system comprised of biocompatible materials that provide for the physiological requirements (e.g., surface attachment, medium exchange, and oxygenation) for the above cells to grow.
An excellent example of the merging interface of cell therapy with tissue engineering is the ex vivo production of human bone marrow. This process illustrates as well the interrelationship between the cell/tissue production methodology and the medical device requirements to properly implement the tissue production.
Although lacking the physical geometry that is a feature of other tissues or organs, bone marrow is a tissue comprised of many different cell types, ranging from different stromal fibroblasts, mesenchymal cells, to stem cells and the other cells of the hematopoietic system. The ex vivo process found to be needed for ex vivo bone marrow growth, was to mimic the natural functional environment of the bone marrow, providing for the controlled nutrient perfusion and oxygenation of the stem and stromal cell components under precise conditions of temperature and medium composition. Key to the success was to provide culture conditions that were concurrently amenable for each of the many different cell types that are found in human bone marrow.
Using this approach of tissue engineering, for the first time, the human stem cells that are found in the bone marrow were able to not only survive in culture, but also replicate to produce more stem as well as more mature progenitor cells. This result is in direct contrast to when hematopoietic stem/progenitor cells have been isolated (e.g., CD-34 selection) prior to the culture process. In this case the stem cells do not grow and the cultures die off over a short period, presumably because heterogeneous tissue interactions have been eliminated.
With the successful production of these bone marrow tissue cells, they can be available to be used as a substitute for bone marrow transplantation. This example is an excellent demonstration of how the lost function of a damaged or destroyed tissue, e.g., bone marrow, can be repaired or restored with ex vivo engineered tissue-specific cells.
Once the basic cell/tissue production process is identified, the next requirement for therapeutic utilization is the need for clinical systems to implement the process. These systems should be amenable for routine use by the thousands of hospitals and clinics in the developed and developing world that serve the patients intended to benefit from the transplantation cells and tissues in native or genetically altered form.